[PATCH dwarves] btf_encoder: fix memory access bugs

[Ihor Solodrai <ihor.solodrai@xxxxx>]

When compiled with address sanitizer, a couple of errors were reported
on pahole BTF encoding:
  * A memory leak of strdup(func->alias), due to unchecked
    reassignment.
  * A read of uninitialized memory in gobuffer__sort or bsearch in
    case btf_funcs gobuffer is empty.

Used compiler flags:
    -fsanitize=undefined,address
    -fsanitize-recover=address
    -fno-omit-frame-pointer

I stumbled on these while working on [1].

[1] https://lore.kernel.org/dwarves/20241213223641.564002-1-ihor.solodrai@xxxxx/

Signed-off-by: Ihor Solodrai <ihor.solodrai@xxxxx>
---
 btf_encoder.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/btf_encoder.c b/btf_encoder.c
index 3754884..520ff58 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -1793,6 +1793,9 @@ static int btf_encoder__collect_btf_funcs(struct btf_encoder *encoder, struct go
 			goto out;
 	}
 
+	if (gobuffer__nr_entries(funcs) <= 0)
+		return 0;
+
 	/* Now that we've collected funcs, sort them by name */
 	gobuffer__sort(funcs, sizeof(struct btf_func), btf_func_cmp);
 
@@ -1954,6 +1957,11 @@ static int btf_encoder__tag_kfuncs(struct btf_encoder *encoder)
 		goto out;
 	}
 
+	if (gobuffer__nr_entries(&btf_funcs) <= 0) {
+		err = 0;
+		goto out;
+	}
+
 	/* First collect all kfunc set ranges.
 	 *
 	 * Note we choose not to sort these ranges and accept a linear
@@ -2607,7 +2615,8 @@ int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu, struct co
 						       ", has optimized-out parameters" :
 						       fn->proto.unexpected_reg ? ", has unexpected register use by params" :
 						       "");
-					func->alias = strdup(name);
+					if (!func->alias)
+						func->alias = strdup(name);
 				}
 			}
 		} else {
-- 
2.47.1